Quantum computers are not a threat for spies or for communications within private organizations where security is considered very important, where the use of public-key cryptography can easily be completely avoided and authentication and session key exchanges can be handled with pre-shared secret keys used only for that purpose.

So practically immediately after DES was standardized, people realized that NSA had crippled it by limiting the key length to 56 bits, and they started to use workarounds.

Before introducing RC2 and RC4 in 1987, Ronald Rivest had used since 1984 another method of extending the key length of DES, named DESX, which was cheaper than DES-EDE as it used a single block cipher function invocation. However, like also RC4, DESX was kept as a RSA trade secret, until it was leaked, also like RC4, during the mid nineties.

IDEA (1992, after a preliminary version was published in 1991) was the first block cipher function that was more secure than DES and which was also publicly described.

Leaf certificates don't last long, but root CAs do. An attacker can just mint new certs from a broken root key.

Hopefully many devices can be upgraded to PQ security with a firmware update. Worse than not receiving updates, is receiving malicious firmware updates, which you can't really prevent without upgrading to something safe first.